1. Field of the Invention
The present invention relates to a semiconductor processing system including a vaporizer for generating a process gas from a liquid material, and particularly to a system comprising a film formation processing apparatus for performing, e.g., ALD (Atomic Layer Deposition), MLD (Molecule Layer Deposition), or low pressure CVD (Chemical Vapor Deposition). The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
A film formation process for forming a predetermined film on the surface of a semiconductor wafer is performed in manufacturing semiconductor devices. For example, a process of this kind is performed, using a low-pressure CVD apparatus. In low-pressure CVD apparatuses, a source material is supplied in a gaseous state to promote a chemical reaction, thereby depositing a thin film on the surface of a wafer. In apparatuses of this kind, there is a case where a process gas is generated by vaporizing a liquid material, and is supplied into a process chamber as a film formation gas. For example, in order to vaporize a liquid material, there is known a structure including a carrier gas supply passage formed concentrically around a liquid material supply passage. These supply passages are connected to a nozzle at their lower ends, from which a liquid material and a carrier gas are delivered to atomize the liquid material into mist by means of a nebulizer action. Then, the atomized liquid material is heated and thereby vaporized.
In a nozzle of this spray type, the pressure inside the vaporizing chamber needs to be lower than a pressure limit value for vaporizing the liquid material, and thus, conventionally, the pressure inside the vaporizing chamber is preferably set to be as low as possible. On the other hand, recently, since semiconductor devices need to use high-dielectric constant thin films, studies have been made on vaporization of a liquid material comprising a solid material, such as Sr(THD)2 (strontium bistetramethyl-heptanedionato) or Ti(MPD)(THD)2 (titanium methylpentanedionatobistetramethylheptanedionato), or a high viscosity liquid source, such as Sr(METHD)2 (strontium bismethoxyethoxytetramethylheptanedionato), dissolved in a solvent. Where a liquid material of this kind is vaporized, if the flow rate of the liquid material is too small, the pressure inside the vaporizing chamber becomes too low, and the solvent or thinner may be preferentially boiled in the tip of the nozzle. In this case, the solute of the liquid material is precipitated in the tip of the nozzle and causes nozzle clogging and/or spray abnormality. Consequently, residues are increased due to a deterioration of the vaporizing efficiency, and case particle contamination on wafers.
Conventionally, semiconductor processing systems including a gas supply apparatus using a vaporizer of this kind are arranged such that the structure and use conditions of the gas supply apparatus are preset in accordance with a liquid material, and the pressure of the vaporizer is not controlled independently of the semiconductor processing apparatus. However, in order to prevent problems from being caused by the new liquid materials described above, there has been proposed a structure that includes a pressure sensor for monitoring the pressure inside the vaporizing chamber (Jpn. Pat. Appln. KOKAI Publication No. 2002-324794 (Patent Document 1: page 5, paragraph 2, and FIG. 1)). According to the invention disclosed in Patent Document 1, the pressure inside the vaporizing chamber is monitored by the pressure sensor, so that, when a decrease in the pressure inside the vaporizing chamber is detected due to progress of clogging in the tip of the nozzle, the liquid material is stopped to interrupt the film formation process. Then, a solvent that has a vaporizing temperature higher than the solvent of the liquid material is supplied into the feed line to stop drying of the interior of the feed line and to clean the interior of the feed line by dissolving an organic metal derived from the liquid material and precipitated due to a decrease in the pressure inside the vaporizing chamber. Consequently, the tip of the feed line can be prevented from being completely clogged, so as to eliminate a working operation time of about two days for replacing the feed line, thereby improving the productivity.
However, according to the invention disclosed in Patent Document 1, when a decrease in the pressure inside the vaporizing chamber is detected during a film formation process, the substrate being treated by the film formation process is suspended halfway. Then, this substrate is discarded, because this substrate may be contaminated with particles of e.g., the organic metal precipitated due to a decrease in the pressure inside the vaporizing chamber. Accordingly, the invention disclosed in Patent Document 1 can safely stop the apparatus to prevent the feed line from being completely clogged when the pressure inside the vaporizing chamber is lowered, but needs to discard the substrate being treated by the film formation process and to reset the process with a new substrate.